Sand shell-moulding method for the production of a part for use in the automotive and aeronautics fields

ABSTRACT

A sand shell-moulding method for the production of a part for use in the automotive and aeronautics fields, in which: a metal or alloy is poured into the shell mould in order to produce a part; the shell is forcibly and rapidly cooled; and an operation of decoring of the part is realized.

TECHNOLOGICAL FIELD

The present disclosure relates to the foundry technical sector, notably to alloys of aluminum, magnesium, copper or other similar materials. More particularly, the present disclosure relates to a sand shell-moulding method, for the production of a part for use in the automotive and aeronautics fields.

BACKGROUND

The sand shell-moulding method is well-known to a person skilled in the art.

It consists of using sand, pre-coated with a thermosetting resin which, in contact with a pattern plate, heated to a temperature of around 200° C., hardens over a layer of a few millimeters, constituting the shell. Each shell corresponds to a half-mould, which is then polymerized, then glued.

Among the various sand shell-moulding methods, mentioned may be made of Croning, hot box, cold box, warm box, inorganic, etc).

This moulding method has several advantages, among which mention may be made of the possibility of producing very complex geometries, as well as the possibility of integrating various functions onto the part in question, for example an exhaust manifold on a cylinder head for motor vehicles. Other advantages are to be noted, for example, the reduction in weight of the parts obtained. Such a method requires, furthermore, low investment, and enables the number of machining operations to be reduced.

In contrast, the parts obtained by this shell-moulding method have mechanical characteristics, which are not always satisfactory in certain fields of application, considering the very low solidification rates.

It would appear, therefore, that a shell-moulding method is particularly well-suited to the manufacture of complex geometrical parts, when these parts do not require good mechanical characteristics.

Yet, it has emerged that not only is the geometry of parts becoming increasingly complex but the mechanical characteristics of such parts must reach high levels, in order to meet specifications.

From this prior art and this situation, it therefore seems important to be able to improve the sand shell-moulding method, in order to be able to obtain parts with very complex geometries, having good mechanical characteristics.

SUMMARY

To overcome such a problem, a sand shell-moulding method has been designed according to which, in a first embodiment:

-   -   a metal or alloy is poured into the shell in order to produce a         part,     -   the shell is forcibly and rapidly cooled,     -   an operation of decoring of the part is realized.

Such a method has particularly advantageous application in the automotive and aeronautical fields, for the production of very complex parts, requiring very good mechanical characteristics. The sand shell is manufactured, in a known way, according to a method adapted to the nature of the part to be obtained (hot box, cold box, warm box, 3D printing, etc.). The shell thicknesses are also adapted, according to the characteristics of the part to be obtained, in order to reach the best possible compromise between the metallostatic pressure and thermal resistance of the interface.

DETAILED DESCRIPTION

As indicated, after having poured the metal or alloy, the sand shell, containing said metal or said alloy, still in a liquid state, or in the solidification phase, is then cooled, for example, via quenching. In a known manner, this quenching can be by means of water, oil, air, or any other means enabling such cooling. Rapid and forced cooling means that the shell is quenched while the alloy is still liquid. By way of a non-limiting example, the quenching temperature is lower than 100° C.

These two operations of pouring and cooling have a two-fold benefit, which is, firstly, to enable the orientation of the solidification front by establishing, during quenching, a thermal gradient, and secondly, to increase the solidification rates, and consequently, the mechanical characteristics of the resulting part.

The part then simply needs to be subjected to a conventional decoring operation, said decoring may be chemical, thermal or mechanical.

In another embodiment of the method, a metal or alloy is poured into the shell in order to no longer produce a final part, but rather a preform. The profile of the shell is, obviously, consequently adapted. Then, as previously indicated, the shell is cooled, in a forced and rapid manner, and an operation of decoring of the preform is realized.

In this embodiment of the moulding method, the preform is subjected to a combined pressing and forging operation, as based on the method known under the brand COBAPRESS. This COBAPRESS method is based on, for example, the teachings from patent EP 0 119 365.

This sand shell-moulding method, according to this disclosure, enables mechanical characteristics to be obtained which are considerably better than those obtained in the case of a sand shell-moulding method, according to the prior art, as the test results below show, carried out with the same type of metal or alloy.

Shell Moulding Method According to the Prior Art:

-   -   SDAS: 60-70 μm     -   Rp0.2=200-220 MPa     -   Rm=240-260 MPa     -   A %=1-2%

Shell Moulding Method According to the Present Disclosure:

-   -   SDAS: 30-35 μm     -   Rp0.2=220-260 MPa     -   Rm=290-310 MPa     -   A %=6-8%

formulae wherein SDAS corresponds to the interdendritic space, Rp to the elastic limit, Rm, to the mechanical resistance and A % to the elongation.

It appears from the characteristics of the method that the method combines the advantages of pouring into a sand shell making it possible to obtain parts having complex geometries, with a decrease in weight, reduction in machining operations, while requiring little investment, and while having good characteristics, as is shown by the comparative tests above. It is noted also that the application of the COBAPRESS method enables a large reduction in porosities, and of the skin effect. 

1/ A sand shell-moulding method, for the production of a part for use in the automotive and aeronautics fields, in which: a metal or alloy is poured into the shell in order to produce a part, the shell is forcibly and rapidly cooled, an operation of decoring of the part is realized. 2/ A sand shell-moulding method, for the production of a part for use in the automotive and aeronautics fields, in which: a metal or alloy is poured into the shell in order to produce a preform, the shell is forcibly and rapidly cooled, an operation of decoring of the preform is realized, the preform is subjected to a combined pressing and forging operation. 